Various heat transfer recording methods have been known so far. Among these methods, dye diffusion transfer recording systems attract attention as a process that can produce a color hard copy having an image quality closest to that of silver salt photography (see, for example, “Joho Kiroku (Hard Copy) to Sono Zairyo no Shintenkai (Information Recording (Hard Copy) and New Development of Recording Materials)” published by Toray Research Center Inc., 1993, pp. 241-285; and “Printer Zairyo no Kaihatsu (Development of Printer Materials)” published by CMC Publishing Co., Ltd., 1995, p. 180). Moreover, this system has advantages over silver salt photography: it is a dry system, it enables direct visualization from digital data, it makes reproduction simple, and the like.
In this dye diffusion transfer recording system, a heat-sensitive transfer sheet (hereinafter also referred to as an ink sheet) containing dyes is superposed on a heat-sensitive transfer image-receiving sheet (hereinafter also referred to as an image-receiving sheet), and then the ink sheet is heated by a thermal head whose exothermic action is controlled by electric signals, in order to transfer the dyes contained in the ink sheet to the image-receiving sheet, thereby recording an image information. Three colors: cyan, magenta, and yellow, are used for recording a color image by overlapping one color to other, thereby enabling transferring and recording a color image having continuous gradation for color densities.
In an image-receiving sheet on this system, a receptor layer for fixation of dyes transferred to the sheet is formed on a support, and besides, a layer having high cushion properties, such as a foam layer made up of a resin and a foaming agent or a porous layer containing hollow polymer particles, is generally formed between the support and the receptor layer with the intention of enhancing adhesion of the image-receiving sheet to a transfer sheet (see, e.g., JP-A-11-321128 (“JP-A” means unexamined published Japanese patent application) and JP-A-2-89690).
JP-A-11-321128 discloses forming an intermediate layer containing hollow particles and a high molecular weight compound having resistance to organic solvent as main components on a support by coating and drying, and subsequently forming a receptor layer by applying a resin coating solution prepared using an organic solvent. Herein, the organic-solvent-resistant high-molecular-weight compound used in the intermediate layer plays a role in preventing the hollow particles used in the intermediate layer from being dissolved by the organic solvent used in the receptor layer. However, the formation of a receptor layer by use of a coating solution of resin in an organic solvent has problems that the sensitivity is insufficient and the cost is high, and it has also been desired to introduce improvements in image defects and densities of transferred-ink images.
Further, the heat-sensitive transfer image-receiving sheet disclosed in JP-A-2-89690 includes a hollow-spherical-pigment-dispersed layer and an image-receiving layer (a receptor layer), but it has a problem that the images after image transfer become blurred. In addition, the cases of using vinyl chloride-series copolymers in receptor layers are disclosed in JP-A-5-193256, JP-A-5-229289, and JP-A-9-131972, but these receptor layers have also been desired to undergo further improvements in view of recent market requirements for rapid processing.